1. Field of the Invention
The present invention relates to a laser processing method and a laser processing apparatus in which an object to be irradiated is bent by being irradiated with a laser beam, and to a method of manufacturing a spring arm that holds at the end thereof a magnetic head for accessing data recorded on a disc.
2. Description of the Related Art
Conventionally, a magnetic disc apparatus has been equipped with a magnetic head that comes closer to a surface of a built-in disc and reads/writes data from/onto the disc.
The magnetic head is held at one end of a so-called spring arm formed of a long metal piece provided with spring force. The other end of the spring arm is coupled to an actuator so that the spring arm can be rotated around an arm shaft by the actuator, while the disc can be rotated by a motor. Accordingly, the magnetic head can be freely move above the disc.
Since the magnetic disc rotates so fast in the magnetic disc apparatus, when the magnetic head comes closer to the disc, air pressure is generated which pushes the magnetic head away from the disc and which is inversely proportionate to the distance between the magnetic head and the disc. In addition, the surface of the disc is macroscopically irregular. Therefore, spring force needs to be provided to the spring arm to keep the small distance uniform between the magnetic disc and the magnetic head.
For example, Japanese Patent Laid-Open No. 7-77063 has proposed a technique for causing a long metal piece to have spring force by irradiating the long metal piece with a laser beam at an approximate midpoint thereof in the longitudinal direction, so that the metal piece is bent at the midpoint.
However, the above technique has a problem that an end of the spring arm may be twisted relative to the root thereof around itself in the longitudinal direction. Especially, with such a twisted spring arm, a uniform distance between the high-speed rotating disc and the magnetic disc is hard to obtain.
Incidentally, such a twist may occur not only in manufacturing a spring arm but also in bending any long metal object by irradiating the object with a laser beam at a midpoint in the longitudinal direction thereof.